In recent years, hybrid electric vehicles (HEV) have become increasingly common, and this trend seems likely to continue. Hybrid electric vehicles comprise at least two power units: an electric motor and a further power unit. The further power unit is generally an internal combustion engine (ICE) and typically a petrol engine, although diesel engines, liquid petroleum gas engines or other engines may also be used. The exact means by which the power allowing the vehicle to move is supplied varies depending on the specific vehicle configuration, but all available power units are generally involved. An example of a common power scheme is one in which the electric motor is used to satisfy power requirements up to a given level, and then the further power unit (for example, ICE) is used in conjunction with the electric motor to provide power above the given level. Alternatively, the further power unit may operate even when the power output from this further power unit is not required to move the vehicle, with the power output from the further power unit instead being used to charge one or more batteries, which the electric motor can draw on. Alternative power supply schemes, which may incorporate one or both of the schemes discussed above, can also be used.
As mentioned in the passage above, electric motors in hybrid electric vehicles typically draw on batteries as energy reserves, draining the batteries as they provide motive power for the vehicle. Other energy storage means, such as capacitors or flywheels, may also be used, although battery storage is the most commonly used energy storage means. One example of a mechanism by which the battery may be charged is discussed above, whereby a further engine of the hybrid electric vehicle is used to charge the battery. The battery may also be charged by further vehicle systems, such as regenerative braking systems which store energy recovered during braking in the battery. In addition to (or alternatively to) the battery charging systems discussed above, an external power source may also be used to charge the battery. The hybrid electric vehicle may be connected to a power source such as a large external battery or generator or a mains electric connection via a power cable or other power supply connection (such as inductive charging). The power source can be used to charge the battery, typically while the HEV is stationary (for example, if the HEV is a personal car, while the HEV is parked overnight), and then the battery charge can subsequently be used to provide motive power. Use of external charging means can allow the battery to be fully charged faster than vehicle-based systems. Further, by using a combination of external power sources and vehicle-based systems, the distance the vehicle is able to travel between refueling/recharging stops can be increased. As such, vehicles that allow the use of both external power sources and vehicle-based systems can be referred to as Range Extender Vehicles (REVs) or Plug In Hybrid Electric Vehicles (PHEVs).
Generally, REVs and PHEVs are configured to draw stored energy from batteries as much as possible, without engaging the further power unit (for example, ICE). This mode of operation is usually more cost efficient than modes which utilize the further power unit to a greater extent, because a unit of energy obtained from an external power source (such as a mains electricity connection) will typically be a fraction of the cost of an equivalent unit of energy obtained in the form of petrol, LPG, diesel, and so on. As a result of this mode of operation, it is common for an ICE to be inactive for a comparatively large portion of the hybrid electric vehicle lifetime, even during periods while the hybrid electric vehicle is in motion.
When an ICE is deactivated, the crankshaft of the ICE will typically stop in one of a limited number of discrete angular positions. For example, where a full rotation of the crankshaft with respect to the remainder of the ICE encompasses the rotation of a given point on the circumference of the crankshaft through 360° about the rotational axis of the crankshaft, the crankshaft may naturally stop with the given point rotated through 90°, 180°, 270° or 360°. The crankshaft is caused to stop at a limited number of angular positions due to the engine geometry, with factors such as the number and arrangement of the cylinders determining the discrete positions. Of course, the use of four discrete angular positions listed above (90°, 180°, 270° and 360°) is simply an example, and other numbers and spacings (including uneven spacings) of discrete angular positions will be engendered by other ICE configurations.
In a traditional vehicle powered exclusively by the ICE, the limited number of crankshaft angular stopping positions would not be a major concern; the ICE would, by necessity, be operational while the vehicle was in operation and therefore the crankshaft would be rotating. However, in hybrid electric vehicles, and particularly in REVs/PHEVs, the ICE will commonly be inactive while the vehicle is in operation. While the ICE is inactive and the vehicle is in operation, the motion of the vehicle (particularly vibrations due to road surfaces over which the vehicle travels) can cause the rolling elements in crankshaft bearings to impact into the bearing races. A cumulative result of these impacts may result in what is referred to as false brinelling, a process whereby the repeated impacts between the rolling elements and the races form wear marks in both the bearings and the races, leads to an uneven wear pattern in the bearing elements and potentially to the premature wear of the bearing. In general, false brinelling may refer to bearing damage associated with fretting, with or without corrosion that results in imprints that appear similar to brinelling, but are caused by a different mechanism, such as vibration or oscillation when the bearing is not rotating.